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https://issues.apache.org/jira/browse/GROOVY-12742?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18140827#comment-18140827
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ASF GitHub Bot commented on GROOVY-12742:
-----------------------------------------
testlens-app[bot] commented on PR #3277:
URL: https://github.com/apache/groovy/pull/3277#issuecomment-6725592140
## ✅ All tests passed ✅
🏷️ Commit: ed15df3625aa7ab662b11418534811b395b68bfe
▶️ Tests: 114727 executed
⚪️ Checks: 26/26 completed
---
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> groovy-contracts: a class invariant makes the trait forwarders and trait
> property accessors of the class return null
> --------------------------------------------------------------------------------------------------------------------
>
> Key: GROOVY-12742
> URL: https://issues.apache.org/jira/browse/GROOVY-12742
> Project: Groovy
> Issue Type: Bug
> Components: groovy-contracts
> Affects Versions: 6.0.0
> Reporter: Scott Murphy Heiberg
> Priority: Major
>
> h3. Problem
> A class-level {{@Invariant}} on a class that implements a trait makes every
> method the trait contributes return {{null}}; a primitive return fails with a
> cast exception:
> {code:groovy}
> import groovy.contracts.*
> trait Named {
> String name = 'x'
> String greet() { "hi $name" }
> int one() { 1 }
> }
> @Invariant({ count >= 0 })
> class Counter implements Named {
> int count
> }
> def c = new Counter()
> assert c.greet() == 'hi x' // greet() returns null
> c.one() // GroovyCastException: Cannot cast 'null' to
> class 'int'
> {code}
> Trait properties are affected too ({{getSize()}} of a trait property {{int
> size}} fails the same way). The interface equivalent, where the class writes
> the method bodies itself, is fine. Reproduced on Groovy 6.0.0 and on master
> (df1fe66ed1).
> h3. Cause
> {{ClassInvariantGenerator.addInvariantAssertionStatement}} weaves the
> invariant call before each {{return}} only when the method body is a block.
> The forwarders and property accessors that {{TraitComposer}} generates in the
> implementing class have a bare expression or return statement as body, so the
> generator fell back to appending the (void) invariant call after it, and the
> forwarder's implicit return value was lost. The same fallback left a
> {{@Synchronized}} body unwrapped, so an explicit {{return}} inside it skipped
> the invariant.
> h3. Fix
> Normalise the body to a block first (the {{ensureBlockBody}} step the
> postcondition path already performs since GROOVY-12084), so the implicit
> return is made explicit and the invariant is checked before each return.
> Trait forwarders and property accessors keep their values and are checked;
> the {{@Synchronized}} explicit-return case is checked as well. Pull request
> to follow.
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